1. Field of the Invention
The invention is related to the field of electromagnetic fluid pumps and in particular to a quiet electromagnetic reciprocating piston fluid pump.
2. Description of the Prior Art
Reciprocating piston electromagnetic fluid pumps for the most part are quite noisy, especially under light loads due to the reciprocating piston hammering against the output end of the housing. One approach to reduce the hammering is to insert a coil spring between the housing and the piston as taught by Wertheimer et al in U.S. Pat. No. 3,381,616; Rouquette in U.S. Pat. No. 3,556,684; and Arai in U.S. Pat. No. 4,306,843. Although the springs taught therein reduced the piston's hammering force at the end of the pumping stroke, they were not entirely successful in reducing the noise generated by these types of pumps. An alternate approach is taught by Brown in U.S. Pat. No. 4,079,436, in which a resilient washer is attached to the end of the housing to absorb the hammering of the piston against the housing at the end of the pumping stroke. Because of the direct engagement of the piston with the resilient washer, the washer had to be made from a rather hard resilient material (Nylon) so that it would have a satisfactory life expectancy. Softer rubber washers were subject to distortion and degradation by the constant hammering of the piston and their life expectancy was too short for practical applications.
Brown, in U.S. Pat. No. 4,832,583, discloses a rubber bumper seal for a low pressure metering pump. The bumper seal is attached to the end of the piston and occludes the outlet port at the end of the piston guide when the solenoid is deenergized and the piston is displaced to its extreme position at the end of the pumping stroke. The sealing of the port at the end of the piston guide prevents fluid from being back-siphoned through the pump.